The present invention is directed, in general, to a method of forming a reverse gate structure and, more specifically, to a method of forming a reverse gate structure with a spin on glass process.
Smaller device size and higher speed of operation are both highly desirable performance targets for semiconductor devices. The overall size of semiconductor devices, such as transistors, have continually reduced in size as fabrication processes for producing various submicron devices have improved. With this overall size reduction, the size of the gate structures have also substantially decreased.
Polysilicon is one material used to form conventional gate electrode structures. However, the use of polysilicon gates, particularly in smaller Complementary Metal-Oxide-Silicon (CMOS) devices, causes several problems. One such problem is known as the polysilicon depletion effect, which affects drive current and device switching speed. This polysilicon depletion effect could be substantially reduced if the polysilicon gate electrode could be infinitely doped. Unfortunately, however, this is not possible. To circumvent this particular problem, the semiconductor manufacturing industry developed processes for manufacturing gate structures comprised of metal, which practically have an infinite (e.g., 5E22/cm3) amount of carriers as compared to conventional polysilicon gates.
One known process used to construct metal gates is a process that includes forming the metal gate in reverse order. In such an instance, a xe2x80x9cdummyxe2x80x9d gate is formed and later replaced with a metal gate. This is desired because the gate dielectric and gate electrodes are created after formation and activation of the source and drain regions. Because of this, high temperatures used to achieve the activation step do not have an opportunity to damage the metal gate.
Conventional reverse-gate processes employ a polysilicon dummy gate, as the dummy gate mentioned above. There are several disadvantages, however, associated with the use of the polysilicon dummy gate. For example, the fluoride etch required to define the polysilicon dummy gate negatively affects any silicon and oxide structures located thereby. This is partially because the fluoride etch chemistry is not sufficiently selective to the polysilicon dummy gate, and attacks the silicon and oxide structures located thereby.
Additionally, when the polysilicon dummy gate is removed, a residual polysilicon stringer is left behind, because polysilicon is irregular in shape. Complete removal of the dummy gate is critical because any residual polysilicon stringers affects the gate length and device performance. In an effort to remove any residual polysilicon and achieve smooth topography, the polysilicon is often over-etched, resulting in damage to the silicon surface in the channel area, and eventually, degradation in the transistor.
Another disadvantage associated with using the polysilicon dummy gate is that the conformal polysilicon film around the isolation structure makes the gate print more difficult.
Accordingly, what is needed in the art is a method of forming a reverse gate structure that address the problems discussed above.
To address the above-discuss ed deficiencies of the prior art, the present invention provides a method of manufacturing a transistor gate structure. In one embodiment, the method includes defining a dummy gate structure comprising a spin on glass on a semiconductor substrate, forming a dielectric layer over the dummy gate structure, removing the dummy gate structure to form a gate opening within the dielectric layer, and forming a gate material comprising a metal within the gate opening.
The foregoing has outlined advantageous and alternative exemplary features of the present invention so that those skilled in the art may better understand the detailed description of the invention that follows. Additional features of the invention will be described hereinafter that form the subject of the claims of the invention. Those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiment as a basis for designing or modifying other structures for carrying out the same purposes of the present invention. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the invention in its broadest form.